Apparatus for stretch bending structural elements



May 25, 1948. w. c. FIELDS EI'AL 2,442,268

APPARATUS FOR STRETCH: BENDING STRUCTURAL ELEMENTS Filed July 16, 1942 4 Sheets-Sheet 1' Will/hm 0. Fields,

. Carpqnfer, 8 G16 Fin/18y Arrows W. C. FIELDS ETAL APPARATUS FOR STRETCH BENDING STRUCTURAL ELEMENTS .May 25,, 1948.

Filed July 16, 1942 4 Sheets-Sheet 2 A'munm E 5 Car/Wen & c. '6. F332;

ma Held;

May 25, 1948. 2,442,268

APPARATUS FOR STRETCH BENDING STRUCTURAL ELEMENTS W. C. FIELDS EI'AL Filed July 16, 1942 4 Sheets-Sheet 3 WCF//ds; EECarnfe/j & c. 45 Fin/re Afton":

y 1948- i w. c. FIELDS EI'AL 2,442,268

APPARATUS FOR STRETCH BENDING STRUCTURAL ELEMENTS Filed July 16, 1942 4 Sheets-Sheet 4 0 T 7 F1 1U. 33

1' 1 11 r'"; LL11; TLLJ INVINTORS we. Fields, 5. E Carpeflfer". G6. Fin/72y I Armulvs Patented May 25, 1948 UNITED NT 2,442,268. EPPARATUS FOR STRET-(JH BENDI'NG: STRUCTURAL ELEMENTS William Carl Fields,l.near. Seattle, Edward-13.. Carpenter, Seattle, and George .G; Einney, near.

Seattle, Wash, assignors to Boeing" Aircraft Company, Seattle, Washa, a corporation of- Washington Application .lul-yil-fi, 1942, Ser-ial No.. 451,160

7*Claims. l.

The bending of structural or framing elements, such as the nose rib chordsoftairplane wings,,the interspar or center wing. rib chords,,the flapcutout ribs, and the like, presents a problem, namely, to avoid wrinkling of. the flange portions of the structural element, particularly the. flange .at the interior of the bend. The problem arises because in the process of bending such an elementin the general plane which includes its web: theibending produces tension forces about the exterior mar-- gin of the bend, and inwardly tea-neutral. axis intermediate its interior and exterior margins;.but likewise producescompressive stresses within the interior margin of thebe-nd,v and; these-compressive stresses, transmitted.- to' the: flanges;, cause wrinkling thereof. Where the curvature is severe; as for instanceg'about the nose: rib chords of' an airplane wing, it has been customary heretofore either to formthe entire-nose sectiontof the-rib as a stamping, or toform it of separately: bent; stringers, and thento. rivet-or-otherwise secure; together these bentstringers ator near the-point of maximum curvature; This, of course, meant: two bending operations: and a securing operatiom. and'the-formation and securement of gussetsv or splices, and therebyincreasedthe cost andiweight; of the part, and limitedseverely the rateofproduction.

The present invention: concernsa method: and" amachine, whereby such: bending of. structural; elements. can be accomplished; whethent'he bend-1 be' severe or slight, ina single:operatiomrapidly: performed, withoutthe necessity; of allowingfor.

spring-back, automatically; straightening parts,

warped from heat-treating; or otherwise, andpres: serving to as high a degree asgmay bet-necessary thev structural strength .characteristicsaand; cross-r sectional shape of the element.

The present, method-resembles; but. must; not;

be confused: with, the; method. of: stretchL-bendingz,

sheet metal, eventhoughzthe.machines used: in:

carrying out the present invention are thelsamez machines as are used. for stretch.-bending-- sheetmetal, with certain modifications. The present.

invention concerns, thebending. f structural-elements, particularly of relatively soft-cmetalsasucl'r: as aluminum; alloys; which elements .have: rela.;-.-

tively deep; webs, that: is to say, -webs of; apprecia: to thew-thickness; oi the. :web:

ble. depth relative material. Suchstructural elements are normally formedby bending or shaping. sheet metallstrips intothe .desired,cross sections They maybesi'nr gleflwebbed. ,or .multiplewebbed, and. in. some in: stancesthe bendmay hei'n such'laplane .thatthe portion of the elementwhich would normally. be considered its-flangebecomesin efiectitsweb. The form usectior purposes ofillustrationirr the accompanying drawingsflsahat section butthe invention. is. applicable. to ,any analogous form. It is also applicable to extrusions .aswelLassheet. metalelements, thatis to .say, to. any element capable, of, appreciable permanent elongation. or stretching. withoutrupt'ure. or. .undue. weakening.

The method. hasbeen used, on aimodifiedlhat. section.v (the. flangesrwhereofjare turnedlup .to a depth of T e") of .032 No. 24" S. Q...ali1minum alloy thewebspacing being. /2, andlit's depth L", with flangea. It hasalsonbeen. usedeona hat sectionof. N0..2'J,,S;;Ou aluminumalloy 6." deep, 4!. wide, and hailing L /iffflangesh Other, sections. canbe. bent, and other materials.; ans, nealed stainless steel. has been.v successfullybent by. c this, process, The. noselrib: chords. illustrated represent about the shortest radius which itnis practicable. to bend. thus; in general, all contours encountered in, normal aircraft. wings can-.be so; bent.

Briefly,lthe method-consistsin applying bending, forces to suchan: element, in. the general planeof, its web and simultaneously; applymg or maintain-. ing apreviouly applied tensional force. in axdircction. and; combinediwith the -tensional-comnonent.

' of, the bending; force,- of a; value-to .elongatethe:

k inathe. element (is; to neutralize.- the compressi m out; the .entireilengthi ofspthe; strllcturaleelementwz insidezof thainteriormargin;.of thabends.

The, actual; ermanentaelonsetionlofi --thee .1epmeat shouldloccur-not laterrthan therapphcatlbni.

of bending forces, and may occur prior thereto. The elongating force is, therefore, of a value sufiicient, by itself, to effect elongation, without adding to it the tension component of the bending forces, or so nearly sufficient that a. very slight addition from the tension component will efiect permanent elongation.

One of the principal advantages of the method is that the work is bent directly and precisely to the desired shape or contour, and no allowance is required for spring-back.

The method is conveniently carried out by modification of machines already available, such as are shown in the accompanying drawings in various forms. These drawings are largely diagrammatical in character.

Figure 1 is an elevation of the machine set up for the start of the operation of bending a Wing nose rib chord. Figure 2 is a view similar to Figure 1, showing an intermediate stage in the same operation, and Figure 3 is a similar view showing the final stage of the first step. Figure 4 is a similar view, showing, however, a finishing or second step in the formation of the wing nose rib.

, Figure 5 is 'a view similar to Figure 1, showing thestart of the operation of bending an interspar rib chord or stringer. Figure 6 is a similar view showing an intermediate stage of the operation, and Figure 7 is a similar view showing the final stage of this operation.

Figure 8 is a view similar to Figures 1 and 5, showing a modified form of the machine, set up for the initial stage of bendin a flap cut-out rib, and Figure 9 is a similar view showing the final stage in this operation.

Figure 10 is a view similar to Figure 5, showing a modified form of the machine for performing the same operation. Figure 11 is a similar view, showing an intermediate stage, and Figure 12 is, a similar view showing the final stage of this operation.

The invention will be best understood by following through a representative operation, such as that shown in Figures 1 to 4 inclusive. The work may be preliminarily heat-treated and chilled, or if the bend is not too severe this may be omitted. The structural element, or work W, is clamped and held by any suitable means, such as theclamps represented at 3| and 32. Any suitable form of clamp or releasable securing means may be employed. Preferably it is of such type as will clamp the tighter With increasing tension. Each such clamp is pivoted at an to some immediate support, which in the form shown in Figures 1, 2, and 3 is an arm or link 4| or 42. The clamp is supported from a fixed (though preferably adjustably positioned) support, such as the shiftable slides 45, 46, supported in the bed frame 5, the support being by means such as the links 43, 44, pivoted to their respective links 4| and 42 at 40, and'to their respective slides 45, 46 at 49. The pairs of links 4|, 43, and 42, 44, thus become toggle links, and in the initial position of the parts shown in Figure 1 they assume a relative dog-leg position.

'A form 1 of suitable material (hard board suitably reinforced has been used, or steel), having a marginal groove U shaped to receive at least the web portion of the element W, has a curvature corresponding to and preferably identical with the desired final shape. This form is interposed between the fixed supports 45, 4B, and is capable of movement, in the general plane of'the web of the'stru'ctural element W, and in a direction transverse to its extent as His held sheet metal stretch-forming machines.

between the clamps, to engage the structural element and to bend it. Thus the form I may be supported upon the table 2| of the plunger 22 of a hydraulic jack or jacks 2.

Since preferably the elongation of the structural element W is accomplished by and during the upward movement of the form (although as is illustrated in Figures 10, 11 and 12, it may be accomplished by independently operable means), it is preferable to connect the toggle linkage to the form, or to the press table, which in efiect becomes part of the form for such purposes. To this end the links 4|, 42 are pivotally connected at Ill to the form adjacent its upper end. It will be recognized that the jack 2, the bed frame 5, and the form together with a means to hold down the extremities of the work to the bed frame, is substantially identical with The toggle linkage, however, and its operation, as will shortly be described, and the bending of deep-webbed structural elements by such machines, has not been accomplished heretofore,

to our knowledge.

In starting such an operation, then, the element W which is to'be bent is clamped by its opposite ends in suitably formed clamps 3|, 32, controlled by the handles 33 and 34. To support the open interior of the illustrative hat section against inward collapse of its thin walls it is desirable to insert a filler, such as the flexible chain C, which may be formed or fiber or like material. Except for completion of the insertion of the filler C the apparatus is substantially ready to initiate the bending operation, as it is set up in Figure 1.

To initiate the operation the form is moved upwardly in this instance, and the first result is to stretch and permanently elongate the element W, even before the web of the structural element W is fully received within the marginal groove or channel ll of the form. Upward movement of the form with respect to the fixed supports 45, 46 immediately causes separation of the clamps 3|, 32, measured along the work, by reason of the movement of the toggle links of the respective pairs towards alignment. The linkage is so calculated and designed that this separation of the clamps efiects permanent elongation of the work. This elongation does not necessarily occur in all parts of the length of the element throughout all stages of the operation, nor does it necessarily occur to an equal degree in all parts of the length. These factors are controlled by proper design of the linkage or equivalent elongating devices, of the form, its radius, and the like, as will be apparent to the designer. However, wherever and whenever bending is actually occurring, there and then elongation should also occur.

As upward movement of the form continues, through the position shown in Figure 2, and into the position shown in Figure 3, the stretching and the simultaneous bending continues, and the structural element takes a permanent set. Care is-taken that the bending is not so severe as to materially weaken the form, which, of course, can be provided initially with excess strength, if that is found necessary. In the position of Figure 3 the pivots 49, 40. and In, which viously had been arranged in a crossed orscissors relation, are now nearly in alignment, drawing the ends of the structural element inwardly towards'the bottom end' of the forms periphery.

Due to mechanical limitations it has been found; simpler to efiflect the complete bend of a nose rib chord in two operations, rather than in asingle operation, and the final operation is shown in Figure 4. The structural element, bent totheshapeshow-n in Figure 3, is reengaged by the clamps 3| and 32, carried by the toggle links M, 43, and 4 M, respectively, with the fixed supports, such as that illustrated at '35, adjusted inwardly, and now upward movement of the form l tends to move the pairs of toggle links into or towards alignment with each other within the respective pairs, and thereby draws inwardly the clamps 3i, 32, further stretching and elongating the structural element W while atthe same time bending it to conform to the shape of the form I.

sloping of the flanges, to accommodate the sweep-back of the wings leading edge, can be accomplished all in the same operation, without appreciable wrinkling, for the metal is or can be substantially Wholly in tension, and the tension can be sufiicient to stretch that flange which requires it for such sloping. The forms may have flats, for junction of stringers, and the work can be struck with a mallet, after or during bending, to apply these flats.

Figures 5, 6, and 7 illustrate a bend which is relatively slight, but which, because it is slight, is difficult to accomplish. Because there is so small a tension component of the bending force, substantially all the tension required to displace the neutral axis inside the interior margin of the bend, and to make the structural element W conform throughout the length of the form la, without spring-back, must come from the longitudinal stretching. It has been found necessary, therefore, to efiect greater elongation oi the structural element, and in this instance in particular to effect its elongation previously to applyin any bending force to it, and to maintain that elongating force at a relatively high value during the bending to assure that the material will exceed its elastic limit during the bendin operation, and consequently that the element will preserve its bent formation without springback. While in bending to such a curvature as is shown in Fi ures 1 toe it may also be necessary to effect elongation previously to effecting any bending, this is required to an appreciably greater degree in efiecting a slight curvature throughout a long structural element or" the nature shown in Figures 5 to '7.

The result is accomplished, as in the previous example, by an arrangement of toggle links such as is shown in Figure 5. The clamps 3!, 32 are supported as before from one of the toggle links Ma or 43a, or, in the other pair, 420. or Ma. In effect, the clamps are supported by the common pivot 35 between the two links of each pair. One such link is pivotally supported at 59 to an adjustable but now fixed support 55 or 45, and the other link of the pair is pivotally connected at H] to the form la or to the table 2 i which, so far as the method is concerned, is in effect a part of the form. The initial position is shown in Figure 5, and by comparison of Figures 5 and 6 it can be seen that prior to any contact of the form la with the structural element W, and, of course, prior to any application of bending forces to the structural element, there has been appreciable and permanent elongation of the structural element effected by stretching it to stress the material beyond its elastic limit. As upward movement of the form continues the elongation of the struc- ,eigh hour shift, by two operators.

tural element continues, until; par-ts, reach the final position shown in Figure 7.

It; may be noted here. that" the structural element can be released from its clamp either, by manipulation of the handles; 34;-or by shipping the structuralelementv justv inside of one of its clamps, particularly in the arrangement shown in Figuresb to'l. In the latter case" the tensionin the structural element causes; any fracture to continue almost instantaneously; and to sever the structural element between; the form and the clamp, after which it isireadily removed from the form.

This particular piece can be turnedout at the rate of '75 an hour (using dual forms), as compared to 3' or 4' an hour, using the-oldsystem of forming on the draw former and hand-working to contour. I his prior system required allowance for spring-back, and because of diiference in spring-back in diiierent lots of material the parts could never be quite accurate. The present method forms to precise shape, and there is; no spring-back, hence it not only promotes speed but also accuracy and uniformity.

The arrangement shown in Figures 8v andQapplies the stretching forces otherwise than through toggle linkage, and alsodiiferentially as between the two ends of the structural:- element. Here links 4? and 58. support the'clamps, 3|- and 32, respectively, at their swinging ends w-hile their other-ends are fixedly pivotedat 49, to the fixed supports 45 and Adrespectively. The swinging ends of these arms-carry camfollowers 6| and 62, which engage in and are guidediby cam-slots 6,3, and 6 respectively, formed in acam plate 6, placed alongside of and preferably secured to the form lb.

The form lb is shaped to provide the most severe curvature at the left-hand end, as viewed in Figures 8 and 9. It; isnecessary to effect more elongation proportinately at-this, end of the struc tural element than at its opposite-end, therefore the cam slots 63 and Mare differentially shaped, to the end indicated. The camslot E l-maybe. in effect substantially an epicyclic curve with respect to the curvature of the right-hand end of the form ib, and the effect of this is to hold the structural element, particularly after an initial elongation, which occurs prior togengagementiof; the work'with the form, against further elongation, while still holding the. workv tensioned. At: the left-handend, however, the cam slot 63, is formed to effect initial elongation, andEin addir tion to effect continuing. elongation between; the clamp at at this end: and thepoint-of maximum curvature, oribetwe'enzthe clamp and. the point of tangency of the work to ther-form.

By the use of dual forms on-a Yd-ton stretch press, 800 such pieces can be completed; inan Previously they had been formed. with hammer dies, thenhea-t-treated and: straightened by rehitting, the parts, and then flattened in still another opera tion. The present processrepresents:a1 large gain in speed, efficiency, and economy.

In all forms, but, inthis form in particular,- itwill be evident that the. form mightb'e held, and that the supports and 45, which have been termed the fixed supports, might be movable in.-'

stead with relation to the fixed form. It is also,

' clear that the movement ofj the clamps-with re- In the forms heretofore described the stretching of the structural elements has been caused by the relative movement of the form and the fixed supports, although the stretching is a separate and independent or additional force besides the bending force. In the arrangement shown in Figures 10, 11 and 12 the stretching force is wholly separate from and independent of the bending force, and can be applied at any stage of, prior to, during, or after the application of bending force. Also the stretching force is accomplished in this arrangement, not by cam means or toggle links, but by fluid pressure means.

The form [0, its support, and its moving means .may all be the same as that previously described. "The structural element W is held between the clamps 3| and 32, as before. The pivot 30 for the clamps is supported, however, from the plungers ill and 12, respectively, of fluid-pressure jacks l, which are pivoted at 49 to the respective fixed :supports 45 and 46, adjustable laterally on the :main frame 5. A supply line with a check valve '13 runs to each jack, and fluid can be drained "therefrom under control through the drain line .19 in which is a pressure reducing valve 18.

.At the outset of a bending operation the work W is secured by the clamps 3| and 32, and the next step may be the application of pressure to the jacks 1, to separate the clamps 3i and 32, and thus to stretch and permanently elongate the structural element W stretched between the clamps. The disposition of parts can be seen in Figure 11, and the stretching can be observed by comparison of this figure with Figure .10.

The next step is to apply bending forces to the stretched structural element by relative movement of the form lc. With the additional tensioning component of this bending force it may be that the total tension in the structural element will exceed that necessary to effect the proper set in its bent shape. The arrangement shown permits automatic slacking off of the total tension in the structural element, the pressure relief valve 18 acting to prevent the total pressure within the hydraulic cylinders exceeding the amount for which the valve 18 is set. This value, of course, is readily set or changed at will. It may happen, then, that the plungers H, 12 are permitted to approach one another rather than to separate during the bending action, and yet the objective is accomplished of maintaining a sufiicient total tension in the element that the neutral axis of the structural element is displaced substantially to or inwardly of the interior margin of the bend.

Various forms of mechanism and various modifications of the method have been described, yet clearly various others may be devised which still embody the present invention. The methods and machines herein described are therefore to be takenas illustrative only, and not as restrictive of the scope of the invention, and its scope is not to b restricted except as may be specified in the claims.

What we claim as our invention is:

1. A machine for bending elongated deepwebbed structural elements, comprising a pair of spaced fixed supports, a pair of clamps and a link supporting each clamp from its corresponding support,for movement relative to the latter, a form interposed between the fixed supports, shaped to the desired curvature, means to move said form transversely into engagement with the clamp-held element, to bend it in the general plane of its web, and a pair of arms'each secured nected at its opposite end to the respective clampsupporting links, and by transverse movement of the form cooperating as a toggle linkage with the corresponding clamp-supporting link to efiect permanent elongation of the element during bending.

2. A machine for bending elongated deepwebbed structural elements, comprising a form shaped to the desired curvature, and vertically movable, a fixed support at each end of the form, two pairs of toggle links pivotally connected by horizontal axes, one pair at each end of the form, one link of each pair being pivotally connected to the form, and the other link of each pair being pivotally connected to the adjacent fixed support, the two links of each pair being arranged, prior to initiation of bending, in dog-leg relation, two clamps, one carried by one link of each pair, for securement to opposite ends of the structural element, and means to move the form vertically relative to the fixed supports, thereby shifting the form-carried link pivot, and moving the toggle link pairs towards aligned position, to stretch the structural element.

3. A machine for bending elongated deepwebbed structural elements, comprising a form shaped to the desired curvature of such an element, holding means engageable with one end of such element to resist lengthwise pull on the element, an arm pivotally connected at one end to said form, a second holding means carried by the swinging end of said arm, for engagement with the end of said element remote from that end which is engaged with the first holding means, said arm and form being relatively proportioned and arranged so as to incline said arm from its pivot upon the form outwardly at a small angle to each successive tangent to the form which the element makes throughout a major portion of the bending, a support, the form and said support being relatively movable transversely of the element, a link pivotally connected between the support and said arm, and in the initial rectilinear condition of such element being disposed at an inward inclination towards the form, the link and arm being relatively proportioned and arranged to swing said arm towards the form upon relative movement of the form and support, to bend the element about the form, and coincidentally to stretch the element during bending.

4. A machine for bending elongated deepwebbed structural elements, comprising a pair of spaced-apart supports, a pair of holding means each engageable with one end of such an element, a link supporting each holding means from its corresponding support, for movement relative to the latter, a form interposed between said supports, shaped to the desired curvature, means operable to efiect relative movement between said form and said supports, to engage said form with an element so held, and to bend such element in the general plane of its web, and a pair of arms each secured at one end to the form, and each operatively connected at its opposite end to the respective links, and by such relative movement of the form and supports cooperating as a toggle linkage with the corresponding link to effect permanent elongation of the element during bending.

5. A machine for bending elongated deepwebbed structural elements, comprising a pair of spaced-apart clamps engageable with the respective ends of such an element, a pair of spaced fixed supports corresponding to the respective clamps, a form interposed between the fixed supat one end to the form, and each operatively con- 15 ports, shaped to the desired curvature, means to move said form generally parallel to the element's web into engagement with the element to bend it, two pivotally joined links, one whereof is pivotally connected to said form and the other of which is pivotally connected to one of said fixed supports, one of said clamps being pivotally mounted upon one of said links, for guided movement therewith during and as a result of, and in predetermined relation to such movement of said form, along a predetermined path away from the other clamp, as measured along the element, to effect permanent elongation of the clamp-held element to a predetermined extent during at least a portion of such movement of the form.

6. A machine as in claim 5, including a second pair of pivotally joined links similarly connected, upon one whereof the second clamp is pivotally mounted, whereby such second clamp is similarly guided and moved relative to the first such clamp.

7. A machine for bending elongated deepwebbed structural elements, comprising a pair of supports, a form curved in a given plane, and located between said supports, means to eiiect relative operative transverse movement in such plane between the supports and said form, to bend a work-piece about such form, a pair of Work-engaging clamps disposed at opposite sides of the form, and two sets of links, the links in each set being pivotally connected to each other and to the support, the form, and the clamp, at the respective sides of the form, the links being relatively sized and. having their said pivotal connection arranged, relative to the curvature of the form, to efieot tensional stretching of the Work-piece as the form and supports are relatively operatively moved.

GEO. G. FINNEY.

EDWARD E. CARPENTER.

WILLIAM CARL FIELDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

